Neural Sensing Circuit With DC Offset Compensation for Stimulus Artifacts
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Solution Overview
Problem
Implantable neurostimulator devices face challenges in accurately sensing neural responses due to stimulation artifacts, which can saturate the sense amplifier circuitry and make it difficult to resolve small-amplitude neural signals effectively.
Innovation Solution
The implementation of differential sensing and DC offset compensation circuitry, along with a common mode voltage reference, helps to subtract common mode voltages and stabilize signal levels, allowing for reliable detection of neural responses amidst stimulation artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stimulation artifacts are present in the sensing circuit, then the stimulator can deliver electrical stimuli to tissue, but the sense amplifier becomes saturated and cannot accurately detect small-amplitude neural signals
Solution Approach 1:
The patent segments the sensing function by providing multiple sense amplifiers with different voltage ranges. A first sense amplifier handles low-voltage neural signals while a second sense amplifier handles high-voltage stimulation artifacts, preventing saturation and enabling accurate detection of both signal types separately.
Solution Approach 2:
The patent introduces a common-mode sense amplifier as an intermediary that measures and subtracts the common-mode voltage component containing stimulation artifacts from the differential signal path. This intermediary measurement allows the neural signals to be recovered without contamination from the artifacts.
2Device complexity
If a single sense amplifier is used to detect both neural signals and stimulation artifacts, then the circuit is simple, but the amplifier saturates during stimulation and cannot resolve small neural signals
Solution Approach 1:
The patent divides the sensing function across multiple specialized amplifiers: a first sense amplifier optimized for low-voltage neural signals, a second sense amplifier optimized for high-voltage artifact measurement, and a common-mode sense amplifier. Each amplifier operates within its optimal voltage range, preventing saturation and maintaining precision.
Solution Approach 2:
The patent dynamically switches between different sense amplifiers based on the current signal conditions. The control circuitry selects which amplifier to use based on whether the dominant signal is a neural response or a stimulation artifact, optimizing measurement precision for each condition.
3Measurement precision
If differential sensing is used to reject common-mode voltages, then noise rejection is improved, but stimulation artifacts still saturate the amplifier input range
Solution Approach 1:
The patent uses a common-mode sense amplifier as an intermediary to separately measure the common-mode voltage containing stimulation artifacts. This measured common-mode signal is then subtracted from the differential output, effectively removing the artifact component while preserving the neural signal and preventing saturation.
Solution Approach 2:
The patent changes the voltage range parameter of different sense amplifiers to match different signal types. The first sense amplifier uses a low voltage range suitable for neural signals, while the second sense amplifier uses a high voltage range suitable for artifacts, allowing each to operate without saturation in its respective domain.
Data Source
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AI summary
The present invention relates to a stimulator device, comprising a plurality of electrode nodes, wherein each of the electrode nodes is associated with a different electrode configured to contact a patient's tissue, a DC-blocking capacitor between each of the electrode nodes and its associated electrode, wherein at least one of the electrodes comprises a sensing electrode to receive a voltage from the tissue, wherein each electrode node associated with the at least one sensing electrode comprises a sensing electrode node, sense amplifier circuitry comprising a first input connected to one of the at least one sensing electrodes and a second input, the sense amplifier circuitry further comprising a differential output comprising a first output and a second output, and DC offset compensation circuitry configured to receive the first and second output, and to produce a DC current, wherein a magnitude of the DC current is a function of a difference of voltages at the first and second outputs, wherein the DC current is provided to the first input to adjust a DC voltage at the first input equal to a DC voltage at the second input.